Microstructural evolution and room temperature mechanical properties of AZ31 alloy processed through hot constrained compression

Abstract

The present study deals with the microstructural evolution and mechanical properties of AZ31 magnesium alloy processed throughout the novel hot constrained compression (HCC) method. AZ31 core specimens constrained by steel sleeves were compressed in the temperature range of 100 to 600 °C at 0.1 s−1 strain rate, up to true strain of 0.6 mm/mm. Similarly, simple compression (SC) tests were carried out on the AZ31 specimens to compare with the HCC ones. The AZ31 specimens failed under SC while the HCC process was successfully conducted without any sign of failure. This phenomenon is attributed to the hydrostatic pressure imposed by the sleeve steel. Moreover, microstructure characterization revealed that the greater strain accommodation in the HCC case is a result of grain refinement due to severe twinning and preceded dynamic recrystallization (DRX) at low and high temperatures, respectively. Nonetheless, the HCC process beyond 460 °C led to grain growth and coarser microstructure as compared to the SC counterparts. Mechanical properties of processed specimens were investigated at room temperature using shear punch tests. Results indicated that while shear strength and formability of HCC products are premier at low temperature deformation, they are attenuated by increasing the temperature beyond 460 °C. This phenomenon is mainly attributed to the different grain size distribution and the effects of γ precipitants.